US2480875A - Navigation system - Google Patents

Description

.sept- 6, 1949- w. J. oBRlEN 2,480,875

NAVIGATION SYSTEM Filed March 20, 1948 Sheets-Sheet l JMC. WKZ 75,66.

INVENTOR. Mae d Ze/f/v Sept. 6, 1949. w. J. oBRIEN NAVIGATION SYSTEM 5 Sheets-Sheet 2 Filed March 2.0, 1948 E MM my #a n te.

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Matte, r mf# W. J. OBRIEN NAVIGATION SYSTEM seppe, 1949.

3 Sheets-Sheet 3 Filed March 20, 1948 wwmaaso/w v INVENTOR. Maw/V J @gew Patented Sept. 6, 1949 NAVIGATION SYSTEM William Joseph OBrien, London, England, as-

signor to The Decca Record Company, Limited, London, England, a corporation of Great Britain Application March 20, 1948, Serial No. 16,125 In Great Britain March 20, 1947 9 Claims.

This invention relates to navigation systems, and has particular reference to a radio frequency navigation system of the continuous phase measurement type which finds particular utility when used as an aid-to the navigation of both fast and slow moving vehicles.

In a copending application led by William J. OBrien on August 27, 1945, for Navigation system, Serial No. 612,987, there is described a radio frequency navigational aid in which there is transmitted from a plurality of spaced points continuous signals of unlike but harmonically related frequencies bearing a fixed multiple phase relation to each other, and in which a mobile vehicle is equipped with means for separately receiving the signals and indicating their multiple phase relation at the location of the vehicle. Us-

ing three or more transmitting stations establishes 4two or more overlapping equiphase displacement eld patterns in which the contours of constant phase relation of each pattern constitute a family of hyperbolae. The geographical position of the mobile receiver is determined by locating on a suitable chart the point at which the measured phase relation obtains, the phase indicators and the chart lines customarily being numbered indentically according to an arbitrary numbering system to facilitate plotting the position of the receiver on the chart.

Because of the precision usually required for the navigation of slow moving vehicles such as surface ships. particularly in congested waters or tortuous channels, it is desirable to produce a very sensitive indication at the receiver. With a given phase difference resolving power in the receiver, an increase in sensitivity is obtained by increasing the spacing in wave lengths at the frequency of phase'comparison of the transmitting stations. With the optimum spacings used in practice, considerable ambiguity is introduced because a receiver circumnavigating the transmitters will encounter identical phase relationships at a number of different locations. With surface ships. a great deal of ambiguity does not detract from the usefulness of the system because of the relatively large amount of time available for taking observations, and because usually the geographical location is known approximately with suiiicient accuracy to resolve the ambiguity. Also it is customary to provide the phase indicators with registers to count and record the total number of cycles of phase change, so that once correctly set, the indicators correctly indicate the position at any place in the field without ambiguity.

However, in the case of fast moving vehicles such as aircraft, the high sensitivity and ambiguity are definite disadvantages. The high sensitivity is normally useless, because the location of an aircraft changes so rapidly that a positional fix to an accuracy of a few yards is meaningless. For this same reason, the ambiguity problem becomes more serious. The present invention is directed to a system of the type referred to which will provide a very sensitive indication for use by slow moving vehicles, and which will provide a much less sensitive indication, with a corresponding reduction in the ambiguity, for use by fast moving vehicles.

It is therefore an object of this invention to provide a radio frequency navigation system of the continuous phase measurement type which simultaneously produces a fine sensitive field pattern and a relatively coarse, less sensitive iield pattern.

It is also an object of this invention to provide a radio frequency navigation system of the character above set forth in which the same signals are 'used for the fine pattern as are used for the, coarse pattern, and in which the choice between th fine and coarse patterns is dependent upon the character of the receiving apparatus used.

It is a still further object of this invention to provide a system of the character set forth in the preceding paragraphs in which two overlapping equi-phase displacement fields are produced by the radiation from three points of three unlike but harmonically related signals bearing a fixed multiple phase relation to each other, and in which a fourth signal of a still different frequency but 'harmonically related to the other frequencies and bearing fixed multiple phase relations thereto is radiated from one of the three transmitters for the purpose of controlling the operation of the receiving apparatus.

It is another object of this invention to provide a system of the character set forth in the preceding paragraph in which the multiple phase relation -cf the beat frequency between the two signals radiated from the one transmitter is held xed in phase relative to the beat frequency between the other two signals.

It is also an object of this invention to provide a receiving apparatus for use with a system of the character above described in which means is provided for comparing the phase of two signals of unlike frequency by converting the frequencies to equality through division of each frequency by the unique factor of that frequency.

It is a still further object of this invention to provide a receiving 'apparatus of the character set forth in the preceding paragraph whichincludes means responsive to a synchronizing signal radiated by the transmitting means for synchronizin'g Athe operation of the frequency dividing means.

It is another object of this invention to provide in a receiver of the character set forth hereinbefore a frequency divider which produces the desired frequency by mixing with :the input signal a beat frequency signal derived by mixing the input and output frequencies.

Other objects and advantages of this invention will be apparent from the following specification read in connection with the accompanying drawings, wherein:

Fig. 1 is a block diagram of the apparatus comprising the master transmitter of the system described herein;

Fig. 2 is a block diagram illustrating one of the slave transmitters;

Fig. 3 is a, block diagram illustrating another of the slave transmitters.

Fig. 4 is a block diagram illustrating the apparatus comprising one form of receiver which may be used in the system;

Fig. 5 is a block diagram of a heterodyne frequency divider used in the receiver;

Fig. 6 is a block diagram of another heterodyne frequency divider;

Fig. 'l is a graph illustrating the mode of operation of the heterodyne divider; and

Fig. 8 is a wiring diagram illustrating the components and electric-al connections used in the heterodyne divider.

Referring to the drawings, there is illustrated in Fig. 1 the apparatus comprising the master transmitter of the system to be described. The master transmitter, sometimes hereinafter designated "station A, comprises an oscillator I il which feeds into a. power amplifier Il, the output of which is passed'through a filter l2 and coupled as shown at I3 to a transmitting antenna It. In the specific embodiment of the invention described herein, the master transmitter preferably radiates a signal which comprises the'sixth harmonic of'A a. given fundamental. The eighth and ninth harmonics of this fundamental are radiated by two slave transmitters as Will be described hereinafter. For the purposes of facilitating an understanding of the operation of the system, a fundamental frequency of 10 kc. has been chosen for use in the following specific description. In Iaccordance with this assumption, frequencies of 80 kc. and 90 kc. are. radi-ated by each of the slave stations, and a frequency of 60 kc. is radiated by the master station. Accordingly, the oscillator I is adjusted to produce a 60 kc. output, and the amplifier I i is tuned to thel same frequency. For reasons which will later become iapparent, the f'llter i 2 is tuned to reject '70 kc. signals.

Slave station B, which is illustrated in Fig. 2, is preferably siutated fifty or more miles from the master transmitter and comprises a receiving antenna l coupled to a 60 kc. amplifier I6 serving to amplify 60 kc. signals received from the master transmitter. The output from the amplifier I6 is applied to a frequency divider il which produces from a 60 kc. input signal a 20 kc. output signal. The 20 kc. output from the frequency divider l'l is passed through an electronic phase regulator lu and applied to a frequency multiplier i9 which produces from the 20 `4 kc. input an output signal of 8o kc. I'he 80 kc. output from the multiplier 6 9 ls amplified by a power amplifier and applied to a transmitting antenna 2 i.

For the purpose of maintaining a fixed multiple phase relation between the 60 kc. master signals and the 80 kc. slave signals, a portion of the 60 kc. signal picked up by the receiving antenna Il is lamplified by a 60 kc. amplifier 22, multiplied to a frequency of 240 kc. by a frequency multiplier 23, and applied to one input of a phase discriminator 24. A small pickup loop near the antenna 2| picks up an 80 kc. signal which is amplified .by an 80 kc. amplifier 26, multiplied to a frequency of 240 kc. by a frequency multiplier 21, and applied to the other input of the phase dlscriminator 24. The phase discriminator 2B com-pares the two 240 kc. input signals and producesk a control potential which varies in accordance with variations in phase of the two input sign-als. This control potential is applied as indicated at 28 to the electronic phase regulator I8 so as to produce a phase shift in the 20 kc. signal passed therethrough in such direction as to nullify the phase change which produced the change inthe control potential.

For a more complete description of the slave transmitting -apparatus and a more comprehensive explanation of the operation of the phase regulating equipment, reference should be had to the -copending application filed by William J. OBrien on August 27, 19425,` for "Navigation system. Serial No. 612,987.

In Fig. 3 there is illustrated the apparatus comprising a second slave transmitter which has been designated "slave station C" and which is spaced from stations A and B fifty or more miles. This transmitter operates to radiate from a transmitting antenna 28 90 kc. signals derived from the kc. master signals and bearing a fixed multiple phase relation thereto. The apparatus at this station is identical to that described in connection with Fig. 2, except for the frequencies to which the components are tuned. The 90 kc. signal is derived by dividing the 60 kc. master signal by two to provide a 30 kc. signal which is then trebled to provide the 90 kc. output. The phase discriminator operates at the least common multiple frequency of 180 kc.

As is explained in detail hereinafter, the master transmitter is arranged to radiate a '10 kc. signal which is used to control the operation of frequency dividing circuits in one form of mobile receiving apparatus. The kc. signal is obtained by mixing a 60 kc. master signal with a 10 kc. signal derived from the kc. and 90 kc. slave signals. The desired fixed multiple phase relations among all of the signals is obtained by controlling the phase of the '70 kc. signal in response to detected phase shifts of the above mentioned 10 kc. signal with respect to a 10 kc. beat note between the 60 kc. and '70 kc. master signals.

Accordingly, there is placed at the master transmitter location a receiving antenna 30 which feeds a pair of amplifiers 3i and 32 tuned respectively to 80 kc. and 90 kc. The amplified 80 kc. and kc. signals received from slave stations B and C are applied to a mixing and rectlfying circuit 33 which produces from these two input frequencies' a 10 kc. output signal. A 60 kc. signal picked up from the master transmitting antenna It by a small pick-up loop 3d is amplified by a 60 kc. amplifier 35 and passed through a manual mixer 33 are both applied to a mixer and detector 81 which produces from the two input signals a A'l0 kc. output. The '10 kc. output signal' is passed through an electronic phase regulator 38 to a 70 kc. power amplifier 39. The power amplifier 39 is coupled to the antenna I4 through a filter Bil tuned to reject 60 kc. signals. Thus, the antenna I4 is caused to radiate simultaneously 60 kc. and 70 kc. signals. Since the 70 kc. signals are derived in part from the master 60 kc. signals, and in part from the 80 kc. and 90 kc. slave signals which are each in turn derived from the 60 kc. master signal, it is seen that the 70 kc. signals bear a true harmonic relation to the master signals and comprise the seventh harmonic of the given fundamental of which the 60 kc. signal is the sixth harmonic.

For the purpose of regulating the phase of the 70 kc. signals. the electronic phase regulator 3B is arranged to be controlled by a control potential derived as indicated at 4i from a phase discriminatcr d2. One kc. input to the phase discriminator is taken directly from the output of the mixer 33, and the other is derived as a beat note between the 60,kc. and '70 kc. signals radiated from antenna It. The '10 kc. signals which are induced in the pickup loop 54 are amplified by a 70 kc. ampliiier and, together with the 60 kc. output from the manual phase adjuster 35, are applied to a mixer and detector 55. The 10 kc. output from the mixer 44 is applied as shown at 45 to the second input to the phase discriminator 42. Changes in phase relation between the two 10 kc. inputs to the discriminator 42 results in a change in the control potential applied at 4i to the electronic phase' regulator 38 so as to cause the regulator 38 to shift the phase of the radiated 70 kc. signal in such direction as to keep constant the phase relation between the two 10 kc. beat notes applied to the phase discriminator 42. Phase shifts introduced by manipulation of the phase adjuster 55 are employed to establish the desired phase relation between the 60 kc. and 70 kc. signals.

The intersecting hyperbolic equi-phase displacement fleld patterns resulting-from the simultaneous operation of the transmitters A, B and C may be used to determine the position of -a mobile vehicle through the use of a receiving apparatus such as is disclosed in a copending application filed by William J. OBrlen on August 27, 1945, for Multiple channel radio frequency receiver. Serial No. 612,991. Described briefly, such a receiver comprises means for separately receiving the 60, 80, and 90 kc. signals; frequency multipliers for converting the 60 and 80 kc. 'signals to a common frequency of 240 kc.; frequency multipliers for converting the 60 and 90 kc. signals to a common frequency of 180 kc.; and phase indicators for measuring and indicating the phase relations between the two 240 kc. signals and between the two 180 kc. signals. It will be seen that the position deiining eld patterns are thus rather sensitive, being based respectively on 240 kc. and 180 kc. f

There is illustrated in Fig. 4 a receiving ap master amplifiers being connected to a suitable receiving antenna 55. The output from the 80 kc, amplifier 48 and the output from the 60 kc. amplier 46 are applied to a mixer and detector 5I which produces a 20 kc. beat note which is applied to one input of a phase discriminator 52. The 60 kc. output from the amplifier 46 is also applied to the input of a heterodyne divider 53 operating to derive a 20 kc. output signal from the 60 kc. input, the 20 kc. output signal being applied to the other input of the phase discriminator 52. The phase discriminator is coupled to a suitable indicator 54 for indicating the phase relation between the two 20 kc. signals.

In a similar way the 90 kc. output from the amplifier 49 is applied to the input of a mixer and detector 55 along with the 60 kc. output from the amplifier 56 so as to produce a 30 kc. beat note. The output from the kc. amplifier 45 is also applied to a heterodyne divider 56 which operates to derive from the 60 kc. input a 30 kc. output. This 30 kc. output and the 30 kc. beat note above mentioned are applied to a phase discriminator 51 which operates to indicate on a suitable indicator 58 the phase relation between the two 30 kc. signals.

The heterodyne dividers 53 and 55 are illustrated in more detail in Figs 5 and 6 respectively, and Fig. 8 shows a suitable circuit. The divider shown in Fig. 5 for deriving a 20 kc. output from a 60 kc. input comprises a mixer 59 in which the 60 kc. signal from the master station is mixed with a 40 kc. signal obtained from a detector 50. The complex output from the mixer 59 is applied to a detector 6i which is adjusted to develop in its output circuit a 20 kc. signal represented by the yenvelope of the rectified cornplex wave. This 20 kc. signal is applied to the discriminator 52 and is also applied to the input of a mixer 62 along with a 60 kc. signal from the master station. The resulting complex wave is rectified and filtered by the detector 50 to produce the 40 kc. signal which is applied to the mixer 59.

The divider shown in Fig. 6 for deriving a 30 kc. signal from the 60 kc.. master signal is similar Yto that shown in Fig. 5 and diiers therefrom in the frequencies to which the various components are tuned, and in using as the second input to paratus for use with the transmitting system hereinbefore described which gives positional data in terms of eld patterns based on kc. and kc. respectively. The receiver of Fig. 4 is accordingly better suited-to use on fast moving vehicles such as aircraft because of the 'lower sensitivity of the indication. The receiver comprises four amplifiers 46, 41, 48 and 49 tuned respectively to 60, 70, 80, and 90 kc., all of the the rst mixer the sum of the output and master frequencies instead of the difference as described in connection with Fig. 5.

Reference to Figs. 4, 5 and 6 will show that the output from the 'l0 kc. amplier 47 is applied tc the heterodyne dividers 53 and 56, the specic point of application being the detector 6i of Fig. 5 and the corresponding detector of Fig. 6. This '70 kc. signal is used to synchronize the operation of the dividers to prevent the introduction of an unwanted ambiguity. Since the divider 53 operates to divide the master signal frequency by three. it follows that there is a possible three to one ambiguity between the 60 kc. input and the 20 kc. output. That this is so may be seen by noting that for a given multiple phase relation between the 40 kc. and 60 kc. signals, there are three different arrangements of the two signals in which the given multiple phase relation obtains and that these three arrangements are spaced electrical degrees with respect to the 20 kc. output frequency. The substantial coincidence in time of the 60 kc. and '70 kc. signals is used to control the operation of the divider circuit. Since this coincidence occurs only once every six cycles of the 60 kc. signal, it is seen that the divider is synchronized in every other possible correct relationship. In the case of the divider 56, synchronization is obtained in every third possible correct relationship.

In Fig. 8 there is shown a circuit which is suitable for the heterodyne divider illustrated by way of a block diagram in Fig. 5. The divider comprises input terminals 63, 6d, and S5, the terminal 65 being common, and the terminals 63 and 64 being connected to the outputs of the 60 and '70 kc. amplifiers respectively. The terminal 63 is connected through a blocking condenser 66 to the primary Winding 6l of a transformer 68. A secondary winding 69 of this transformer has one end connected to the control grid of a triple grid vacuum tube lll. The plate f the tube 'lli is connected through a primary winding li of a transformer l2 to a suitable supply of direct plate potential represented in Fig. 8 by the `llegend HT. The winding 7| is tuned to the desired output frequencyin the assumed case, 20 kc. The plate of the tube lll is also connected through a blocking .condenser 73 to one output terminal le, a second output terminal 15 being grounded.

Between the source of plate supply potential HT and ground there is connected a voltage divider comprising resistances 16, 1l, and 78. The cathode and suppressor grid of the tube iii are connected together and to the common point between resistances 'l'l and 18, this point being bypassed to ground by a condenser 19. YThe screen grid of the tube 'm is connected through a resistance 80 to the common point between resistances 18 and 'il' and also through a blocking condenser 8l to the 70 kc. input terminal 6d. The common point between resistances 'I6 and 'il is bypassed to ground by a condenser 82.

A secondary winding 83 of the transformer 'i2 has one terminal connected to the control grid of a triple grid vacuum tube 86, the output circuit for this tube comprising a primary winding of a transformer 86 which is tuned to 40 kc. The cathode, suppressor grid, and screen grid circuits for the tube 8d are similar to those for tube 'i0 and differ therefrom only in connecting the screen grid directly to the voltage divider and in omitting the connection of the screen grid to the 70 kc. input terminal.

A connection 8l extends between the lower end of the winding 83 and the condenser 66 so that the signal applied to the grid of the tube 8B is the complex signal resulting from the mixing of the 60 kc. master signal with the 20 kc. output signal developed across the tuned winding 1|. A secondary winding 88 of the transformer 86 has one end grounded and the Iother end connected as by a conductor 89 to the lower end of the winding t9. This applies to the grid of the tube 70 a complex wave resulting from the mixing of the 60 kc. master signal and the 40 kc. signal developed across the tuned winding 85.

The resistances 16, 1l, and 18, and the corresponding resistances for the tube 84 are adjusted to apply the proper operating potential to the screen grids, and to bias the tubes substantially to cutoff so that they are operative only during the positive half cycles of the input grid signals.

The tubes thus serve to rectify the input signals.

The magnitude of the '70 kc. signal which is applied to the screen grid of the tube 10 is preferably adjusted to substantially prevent operation of the tube except during the positive half cycles of the 70 kc. signal.

In operation, 60 kc. and 40 kc. signals are mixed in the winding S9. The resulting Signal is rectified by the tube 'iii and the output is applied to the tuned winding 1I to develop thereacross a 20 kc. signal which is applied to the output terminals. The 20 kc. signal is also mixed with a 60 kc. signal in the winding 83 and the resulting complex wave is rectified by the tube 84 to develop across the tuned winding 8E the 40 kc. signal which is mixed with the 60 kc. signal in the windi118 69.

The effect of the 70 kc. signal is preventing operation of the tube le during the negative cycles of the 70 kc. signal produces from the 40 and 60 kc. signals a 20 kc. signal, every other positive maxima. of which coincides with the positive maxima of the 10 kc. envelope resulting from a mixing of the 60 and '10 kc. signals. Mixing this 20 kc. signal with the 60 kc. signal and rectifying the resultant in the detector 86 produces a 40 irc. signal, every other positive maxima of which coincides with the positive maxima of the 20 kc. signal. This is the phasing of the 40 kc. signal relative to the 60 kc. signal which is optimum for producing a 20 kc. signal which is so phased as to cause every other positive maxima thereof to coincide with the positive maxima of the 10 kc. envelope representing a mixture of the 60 kc. and 70 kc, signals. Thus the injection of the 70 kc. signal into the detector 'It insures that the 20 kc. output will always occupy a single one of its three possible multiple phase relations to the 60 kc. master signal.

The above explanation may be more readily understood by having reference to Fig. '7 in which graph A shows the relation between the 60 kc. signal B, the 40 kc. signal 9i, and the 20 kc. signal Q2 which results from rectiilcation of the envelope 93 of the 60/40 kc. complex wave. Graph B shows the 10 kc. envelope s4 corresponding to a mixture of a 60 kc. signal 95 and a 70 kc. signal 9S. Note that the positive maxima of the 10 kc. envelope 95 coincide with every other positive maxima of the 20 kc. signal 92. In graph C the 20 kc. signal of graph A is reproduced at 8l and the 60 kc. signal of graph A is reproduced at 98. The 40 kc. signal 99 results from the rectification of the envelope l 00 of the resulting complex wave. It is this 40 kc. signal which is reproduced in graph A at 9i. Note that in graph C every other positive maxima of the 40 icc. signal 99 coincides with the positive maxima of the 20 kc. signal 91, and that in graph A it is this phasing of the 40 kc. signal which causes the 20 kc. signal 82 to have every other positive maxima coincident with the positive maxima of the 10 kc. envelope 9@ of graph B.

In addition to preventing the introduction of an ambiguity as a result of the frequency division in the receiver, the transmission of a 70 kc. signal from the master station secures a further advantage. Reference to Figs. 2 and 3 will show that the kc. and 90 kc. slave signals are each derived by a process which includes the step of dividing the received 60 kc. master signals. Thus, each time the transmitters are placed in operation, the frequency dividers might start their operation with a different one of the plurality of possible multiple phase relationships existing between the 60 kc. master signal and the derived submultiple thereof. This ambiguity causes no diiculty with a receiver of the character described in the aforementioned copending application Serial No. 612,991 because such a receiver includes means for multiplying the slave frequencies by a factor which is numerically equal to the ambiguity which may be introduced .l by the divider at the slavey station, thus eliminating the ambiguity. In a receiver such as has been described in detail herein, it is necessary that the submultiple frequency which results at the receiver from the division of the master signal frequency bear the proper phaserelationto the beat note between the master signal and the slave signal. The described system for deriving and using the 70 kc. master synchronizing signal insures the maintenance of this required relation.'

The way in which the above mentioned result is obtained is best seen by considering a numerical example. Using as a standard the assumption that the system is operating, that the proper phase relations obtain, and that all phase shifts will be referred to the 60 kc. .master signal as a phase standard, let us assume that the slave transmitter B momentarily goes oi theA air and that upon resumption of operation the 80 kc. signal is advanced 120 from its previous phasing, this advance resulting lfrom the ambiguity present in the slave transmitter frequency divider. The 120 advance in the 80 kc. slave signal produces a like advance in the output from the amplifier 3l. Assuming the 90 kc. signal phase to be unchanged, this results in a 120 retardation in the phase of the 10 kc. output from the mixer 33. The retardation of the 10 kc. beat note produces a like retardation in the output from the mixer 31 so that the radiated '70 kc. signal has its phase retarded 120 from the prior relationship. This retardation is also seen in the output from amplifier 43 and causes a similar retardation in 'the 10 kc. beat note output from the mixer M. Note that the two inputs to the phase discriminator 42 (the 10 kc. beat notes from mixers 33 and Ml have both been subjected to al phase retardation of 120 so that the phase regulating system now operates to maintain this new phasing of the 70 kc. signal.

Considering now the receiver of Figs. 5 and 7, it is seen that the 120 advance of the transmitted slave signal will produce a like advance in the output from the amplifier d8. This causes a 120 advance in the output signal from the mixer 5l so that the 20 kc. signal applied to the lower input of the phase discriminator 52 is advanced 120 in phase. However, the 120 retardation of the phase of the '70 kc. synchronizing signal produces a like shift in the output from the amplifier 41. As will be seen from graph B of Fig. 7, this retardation of the '70 kc. signalv similarly shifts the kc. envelope 94. For the 40 kc. signal 9| and the 20 kc. output signal 92 of graph A to coincide with this new position of the 10 kc. envelope 94, the 40 kc. must retard 120. Assuming that this shift takes place, it is seen that the 20 kc. signal is thereby advanced 120. The validity of the assumption of a 120 retardation of the 40 kc. signal may be seen by reference to graph C wherein it is seen that a 120 advance of the 20 kc. signal 91 produces a 120 retardation of the 40 kc. signal 99.

This it is seen that the 120 retardation of the 70 kc. synchronizing signal advances by a like amount the 20 kc. signal applied to the upper input of the phase discriminator 52. It has been shown that the accompanying 120 advance in phase of the received 80 kc. slave signal resuits in an equal advance in the 20 kc. signal applied to the lower input of the phase discriminator 52. These two shifts are compensating, so that the indication given by the indicator 54 is unchanged.

A similar analysis with regard to the 90 kc. slave signals will show that shifts in the phase of these signals is compensated in the same way.

It has been stated that although the phase' measurements at the receiver are made at frequencies of 20 kc. and 30 kc., the actual pattern is based on kc. and 90 kc; This is also best seen by considering a numerical example in connection with Figs. 4 and 5. Using the 60 kc. signal as a reference, let us assume that the position of the receiver is changed at a constant radius from the master station so that the 80 kc. signal is advanced at the receiver by 8. From Fig. 4 it is seen that this advance of 8 in the received 80 kc. signal will produce an 8 ad- Vance in the 20 kc. signal to the lower input of the phase discriminator 52, while the upper input remains unchanged due to being derived from an unchanged 60 kc. master signal. The indicated phase change is thus equal to the phase change at the slave frequency, and it therefore follows that the pattern is based on the slave frequency and not on the sub-multiple used for the phase measurement. A similar analysis with regard to the kc. signals will show that the other pattern is also based on the slave frequency.

From the foregoing, it will be observed that there has been provided a new Navigation System of the continuous phase measurement type, and that the system described operates to generate simultaneously and with a. single set of transmissions a sensitive field pattern suitable for the accurate navigation of slow moving vehicles, and a coarser pattern better suited to the navigation of more rapidly moving vehicles such as aircraft. Attention is directed particularly to the '10 kc. signal andvits derivation to thereby permit the use of a receiver employing frequency divider circuits without introducing an ambiguity. It should also be noted that the '70 kc. signal serves to automatically compensate the receiver for the ambiguities inherent in the slave frequencies when those frequencies are derived from i cept as defined in the appended claims.

Iclaim:

1. In a radio frequency navigation system including means for radiating from three spaced points three signals of unlike but harmonically related frequencies bearing fixed multiple phase relations to each other, the combination of: means for radiating from one of said points a fourth signal of a frequency such that the difference between the frequencies of the two signals radiated from said one point is equal to the difference between the frequencies of the other two signals; and means responsive to variations in the phase relation between said two differences for regulating the phase of said fourth signal.

2. In a radio frequency navigation system including means for radiating from three spaced points three signals of unlike but harmonically related frequencies bearing fixed multiple phase relations to each other, the combination of: means at one of said points for receiving and mixing the signals radiated from the other two of said points to produce a rst beat note of andere given frequency; means for mixing said rst beat note with the signal radiated from said one point to produce a fourth signal having a frequency equal to the sum of the frequencies of said first beat note and said signal radiated from said one point; means for radiating said fourth signal from said one point; means at said one point for picking up and mixing the signals radiated from said one point to produce a second beat note of said given frequency; a phase discriminator for comparing said first and second beat notes and producing a control potential which varies in accordance with variations in the phase relation between said two beat notes; and phase regulating means responsive to variations of said control potential for shifting the phase of said fourth signal.

3. In a radio frequency navigation system including means for radiating from spaced points two signals of different but harmonically related frequencies bearing a fixed multiple phase relation to each other, a receiving apparatus comprising: means for separately receiving said signals, means for mixing said received signals to produce a beat note of a given frequency, means for deriving from one of said received signals another signal having said given frequency, and means for measuring and indicating the phase relation between said beat note and said other signal.

4. In a radio frequency navigation system includingmeans for radiating from spaced points two signals of different but harmonically related frequencies bearing a xed multiple phase relation to each other, a receiving apparatus comprising: means for separately receiving said signals, means for mixing said received signals to produce a beat note of a given frequency, a first and a second mixer, means for applying to the input of said first mixer one of said signals and the output from said second mixer. means for applying to the input of said second mixer said one signal and the output from said rst mixer, said first mixer having an output circuit tuned to produce an output signal of said given frequency, and means for measuring and indicating the phase relation between said beat note and said output signal.

5. In a radio frequency navigation system including means for radiating from a rst and a second point spaced from each other a first and a second signal respectively of dierent but harmonically related frequencies and including means for radiatingV from said first point a synchronizing signal of a frequency harmonically related to the frequency of said rst signal in such wise that the difference in frequency between said synchronizing signal and said first signal is not greater than the diierence in frequency between said iirst and second signals, and all of said signals bearing iixed multiple phase relations to each other, a receiving apparatus comprising: means for separately receiving said signals; means for mixing said received rst and second signals to produce a beat note of given frequency; a first and a second mixer-detector; means for applying to the input of said irst mixer-detector said rst signal and the output from said second mixerdetector; means for applying to the input of said second mixer-detector said rst signal and the output from said rst mixer-detector, said first mixer-detector having an output circuit tuned to produce an output signal of said given frequency; means for applying said received synchrcnizing signal to said drst err-detector for blocking the operation thereof during the negameans at said first point for receiving and mixing said second and third signals to produce a first beat note of given frequency, means for mixing said first beat note with said first signal to produce a synchronizing signal having a frequency equal to the sum of the frequencies of said first beat note and said lrst signal, means for radlating said synchronizing signal from said first point, means at said first point for picking up and mixing said ilrst signal and said synchronizing signal to produce a second beat note of said given frequency, a phase discriminator for comparing said first and second beat notes and producing a control potential which varies in accordano with variations in the phase relation between said two beat notes, and phase regulating means responsive to variations of said control potential for shifting the phase of said synchronizing signal; and a receiving apparatus comprising means for separately receiving said signals, means for mixing said received first and second signals to produce a ilrst output signal, a first and a second mixer-detector, means for applying to the inputl of said first mixer-detector said received rst signal and the output from said second mixerdetector, means for applying to the input of said second mixer-detector said received first signal and the output from said first mixer-detector, said first mixer-detector having an output circuit tuned to produce a second output signal having a frequency equal to the frequency of said first output signal, means for applying said received synchronizing signal to said first mixer-detector for blocking the operation thereof during the negative half cycles said received synchronizing signal, and means for measuring and indicating the phase relation between said first and second output signals.

7. In a radio frequency navigation system including means for radiating a master signal, a rst slave signal, a second slave signal and a synchronizing signal, all of such signals having different frequencies and all being harmonics of a given frequency, the combination of: means at a first location including a fixed frequency oscillator for producing and radiating said master signal; frequency conversion means at a location spaced from said rst location includlng a receiver for receiving said master signal for producing and radiating said first slave signal; frequency conversion means at a location spaced from said first location for producing from a received master signal and radiating said second slave signal, at least one of said frequency conversion means including a frequency divider; a mobile receiver adapted to receive the radiated signals and to provide a line of position indication; and means at said first location for producing and radiating said synchronizing signal, said last-mentioned means including means for receiving both of said slave signals and means for deriving said synchronizing signal from said master signal and said received slave signals in such a manner as to provide a change in the phase of the synchronizing signal with each change in phase of a slave signal, changes in synchronizing signal phase due to slave signal phase changes corresponding to alternate phase relations in the synchronizing of said frequency divider being such as to produce no change in said line of position indicated by said mobile receiver.

8. In a radio frequency navigation system having a master control unit producing a signal of a given frequency and a synchronizing signal of a second frequency, two slave control umts for producing a first slave signal of a third frequency and a second slave signal of a fourth frequency. all four signals being of different frequenciesand each being a different harmonic of a fundamental frequency, said given frequency and said second frequency having a difference frequency equal to said fundamental frequency, and said third and said fourth frequencies having a difference frequency equal to said fundamental frequency, the combination of a frequency divider circuit controlled by said signal at given frequency in at least one of said slave control units, ambiguous phasing combinations of said rst and second slave signals thereby being equal in number to the harmonic number of said given frequency; means in said master control unit responsive to variations in the phase of the said first and second slave signals for regulating the phase of said synchronizing signals to produce a xed phase relation between a'beat e note signal from said given frequency and said 14 said slave signals irrespective of said ambiguous phasing combinations due to alternate phase relations in the synchronizing of said divider.

9. In a radio frequency navigation system, the combination of an oscillator for producing a signal of a given frequency; a first power amplifier coupled to said oscillator; an antenna coupled to said power amplifier for radiating a first signal ofa given frequency; means for receiving from a distant`location a signal of a second frequency diilerent from said given frequency but harmonically related thereto; frequency conversion means coupled to said receiving means for producing a signal of a third frequency harmonically related to said given frequency; a second powerampliiier coupled to said frequency conversion means; means coupling said second power amplifier to said antenna; means for resonating said antenna to both said given frequency and said third frequency; filter means between said rst power amplifier and the said antenna tuned to reject said third frequency; and lter means between said second power amplifier and said antenna tuned to reject said given frequency, said filter means serving to isolate the crossfeed between said first and second amplifiers to a degree sumcient to so reduce the modulation product of said second frequency as to reduce to a negligible amount interference with said signal received from said distant location.

WILLIAM JOSEPH OBRIEN.

No references cited.

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